Lithography techniques include processes in which, for example, a resist film formed from a resist material is formed on top of a substrate, the resist film is selectively exposed with irradiation such as light, an electron beam or the like through a mask in which a predetermined pattern has been formed, and a developing treatment is then conducted, thereby forming a resist pattern of the prescribed shape in the resist film. These resist materials include positive-type materials in which exposed portions exhibit increased solubility in an alkali developing solution, and negative-type materials in which exposed portions exhibit decreased solubility in an alkali developing solution.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have led to rapid progress in the field of miniaturization. Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used; however, nowadays, KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production of semiconductor elements. Furthermore, research is also being conducted into lithography techniques that use F2 excimer lasers, electron beams (EB), extreme ultraviolet radiation (EUV) and X-rays.
Resist materials are required to have lithography properties such as high sensitivity to the aforementioned light source and enough resolution to reproduce patterns with very fine dimensions. As resist materials which fulfill the aforementioned requirements, there is used a chemically-amplified resist containing a base resin that displays changed alkali solubility under action of an acid, and an acid generator that generates an acid upon exposure. For example, as the chemically-amplified positive resist, resists containing an acid generator component and a resin component having an acid dissociable, dissolution inhibiting group which dissolves under action of an acid generated from the acid generator are typically used.
Resins (acrylic resins) that contain structural units derived from (meth)acrylate esters within the main chain are now widely used as base resins for resists that use ArF excimer laser lithography, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 1). Here, the term “(meth)acrylic acid” is a generic term that includes either or both of the acrylic acid having a hydrogen atom bonded to the α-position and the methacrylic acid having a methyl group bonded to the α-position. The term “(meth)acrylate ester” is a generic term that includes either or both of an acrylate ester having a hydrogen atom bonded to the α-position and a methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of an acrylate having a hydrogen atom bonded to the α-position and a methacrylate having a methyl group bonded to the α-position.
When a positive resist is used, resins which have a structural unit derived from a (meth)acrylate ester which has an acid dissociable, dissolution inhibiting group are used as the acrylic resin (see Patent Documents 1 and 2).
Also, as base resins for chemically amplified resists, base resins containing a plurality of structural units are typically used in order to improve lithography properties and the like. For example, in the case of using a positive-type resist, a base resin is typically used which includes the above-mentioned structural unit having an acid dissociable, dissolution inhibiting group, and further includes a structural unit having a polar group such as a hydroxyl group and a structural unit having a lactone structure.
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2003-241385.
[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2006-096965.